1. Field of the Invention
The present invention relates to a method of manufacturing a composite material of a ceramic powder and a metal powder, the composite material being ceramic-rich on its surface and metal-rich in its inside.
2. Description of the Related Art
Heretofore, ceramic materials have widely been used as mechanical components because of their high hardness and heat resistance. However, ceramic materials are disadvantageous because they are generally poor with respect to toughness. In view of the conventional ceramic materials, there have been proposed and used ceramic composite materials (hereinafter referred to as composite materials) made of ceramic and metal.
If the amount of ceramic in such a composite material is increased for increased wear resistance, then the hardness of the composite material increases, but the toughness thereof decreases, resulting in a reduction in the strength. A conventional solution to this problem includes a composite material (hereinafter referred to as a conventional composite material 1) in which mixed powders of metal and ceramic which have various different composition ratios are laminated stepwise. In addition, a conventional solution includes a composite material (hereinafter referred to as a conventional composite material 2) in which metal and ceramic are combined by cladding, fitting, or shrink fitting.
According to the conventional composite material 1, since the metal and ceramic are fired at largely different temperatures, the ceramic cannot be formed into a dense structure if it is fired at the temperature at which the metal is fired, and the composite material cannot hold its desired shape if the metal is fired at the temperature at which the ceramic is fired because it is higher than the melting point of the metal. Another problem is that the conventional composite material 1 tends to be deformed and cracked as the rate at which the metal and ceramic are densified and the composition-dependent shrinkage vary from temperature to temperature.
The conventional composite material 2 are also disadvantageous in that because there is an interface between the metal and ceramic, heat conduction and stress elastic waves concentrate on the interface, resulting in a thermal stress concentration and a stress concentration.
Carbide and cermet which have widely been used as materials for cutters including throw-away tips, drill bits, reamers, etc. wear rapidly when used to cut workpieces of iron and steel, and cause tip chipping depending the workpiece material cut thereby. It has been customary to coat such cutters of carbide and cermet with a hard ceramic layer by physical vapor deposition (PVD) or chemical vapor deposition (CVD) in order to produce a composite structure of ceramic and metal.
However, the coating process such as PVD or CVD is costly. Furthermore, when a layer coated by this coating process, such as a coated layer on a cutter, has a thickness of about 30 .mu.m, the surface of the coated layer tends to peel off the surface of the base metal.
Japanese patent publication No. 4-24424 discloses the provision of a composite layer on the surface of a base metal, the composite layer comprising a coated layer produced by an arc-evaporated ion plating process and a coated layer produced by a fusion-evaporated ion plating process. However, the disclosed case-hardening technique suffers drawbacks in that it poses limitations on the use and size of objects that can be processed, necessarily results in an increase in the cost, requires a highly sophisticated level of technology for its implementation, and is carried out a complex operation.